An image forming material has been proposed as an effective technology for reusing paper, with which a color-developed state stably persists at a temperature close to room temperature, and also a decolorized state persists for a long period of time at operating temperatures due to a treatment with heat or solvent, by newly adding a decolorizing agent to a composition system containing a leuco dye and a developer.
These image forming materials provide highly stable color-developed/decolorized states for images, and are also highly safe as materials. There are advantages in that they can be applied to electrophotographic toner, liquid ink, ink ribbon and writing utensils, and can be erased by a large-scale processing.
With respect to liquid inks, a decolorizable aqueous ink with a small and uniform particle size and which provides a thick color tone without discoloration has been disclosed (see, for example, JP-A 2002-294104 (KOKAI)).
However, the above-mentioned decolorizable aqueous ink is a pigment particle dispersion-based (emulsion-based) ink, and may induce a clogging of the nozzle when being applied to the ink jet printing. Accordingly, a water-soluble liquid ink which can be applied to the ink jet printing and which also satisfies simultaneously the coloring property of images at the time of printing and the erasing property of images at the time of treatment with heat or solvent has been demanded.